This project makes use of advanced high-resolution models of the atmosphere to simulate weather and atmospheric composition in The Netherlands during measurement campaigns of the Ruisdael Observatory. The measurements of this large-scale measurement infrastructure in The Netherlands offer a unique opportunity to test these models, and to acquire novel insight into the atmospheric processes governing the weather and air quality in The Netherlands. This knowledge is needed for a more detailed weather prediction, for example of extreme weather, improved forecasting of urban air quality, and monitoring of the greenhouse gas emission reductions that are planned for the coming decades.

Tropospheric ozone (O3) is a global air pollutant and an important greenhouse gas. Ozone is produced in the troposphere by photochemical oxidation of volatile organic compounds (VOCs) and CO in the presence of nitrogen oxides. These precursors have large and changing anthropogenic sources and some natural sources may be perturbed by climate change. We need to better understand the factors controlling ozone but this is difficult because of complex chemistry involving a continuum of scales from local to global, and because there is net inflow of ozone from the stratosphere. That we do not understand ozone well enough is reflected by the 4th IPCC report stating that the uncertainty on present-day (radiative forcing from) ozone is larger than that of CO2 and methane! I propose to improve this situation by exploring recently advanced satellite observations of ozone and its precursors to their full advantage. The species NO2 and formaldehyde, closely related to emissions of NOx and VOCs, can be optimally observed from space with sensitivity down to the boundary layer. We will use these measurements to constrain the rapidly changing anthropogenic and natural emissions of NOx and isoprene, the main VOC. Implementing the improved precursor emissions in a global chemistry transport model (CTM) allows us to attribute ozone concentrations to their photochemical sources. We can attribute ozone to its natural origin by determining the inflow from the stratosphere. I propose to do this using assimilated ozone fields based on satellite observations of ozone in combination with accurate meteorological information. An improved understanding of the factors controlling ozone will be highly relevant for climate predictions, that still suffer from large uncertainties in changing emissions and their dependency on environmental factors.

The continuous shadows of passing clouds create rapid (seconds to minutes) variations in the solar radiation reaching the land. These cloud flecks induce fast fluctuations in radiative forcing that trigger a cascade of interacting processes across a wide range of spatial and temporal scales acting in soil, vegetation and atmosphere. Understanding and quantifying these processes require detailed knowledge of soil physics, plant biology, atmospheric composition, radiation, turbulence, boundary-layer and cloud dynamics. The challenges are twofold: first, there is a knowledge gap since little is known on how these processes interact across scales and different domains. Second, our weather and climate models are progressively able to resolve smaller and shorter spatial and temporal scales. Thus, they enter the domain where the fast cloud induced interactions act on the surface energy, water and carbon dioxide fluxes which, in turn, feedbacks on cloud formation. Consequently, appropriate parameterizations of these processes need to be designed and tested. In CloudRoots, we aim to develop a unique combined observation - simulation system that allows to quantify all necessary interactions between soil, vegetation and atmosphere, from the size of the stomata (10 - 100μm) to the size of the atmospheric boundary layer (~1 km), while accounting for second to minute scale dynamics as well as diurnal and seasonal cycles. CloudRoots innovates by integrating recent advances in the atmospheric science field. Observationally, we plan new measurement of one-minute fluxes of the water and carbon stable isotopes by combining laser spectroscopy with the scintillometer technique. Numerically, we plan high-resolution experiments using large-eddy simulations including three-dimensional radiation perturbations by clouds and canopy. These novel elements are methodologically divided in two interlinked sub-projects; one is focused on processes and the other on scaling. The processes project (PhD1) is oriented to soil-vegetation-atmosphere interactions in which there will be a prominent role of surface observations. By building on these observations, the scaling project (PhD2) derives relationships of the land processes to larger spatiotemporal scales using a hierarchy of models. The scaling laws provide a basis for parameterizations that will be systematically evaluated in grassland and forest ecosystems of the Ruisdael Observatory in the Netherlands. Once established and evaluated, our scaling relations will be studied in a boreal and a tropical forest sites. CloudRoots will lay the observational and theoretical foundation necessary to include spatiotemporal scale processes in weather and climate forecasts and improve predictions of extreme events.

The power grid in the Netherlands has to accommodate more and more production of solar energy. Due to the erratic nature of incoming solar radiation, fluctuations in the grid arise that could cause instability. In Every Ray Counts (a collaboration between Wageningen University and Alliander), we have worked on better integrating meteorological knowledge into grid management in order to help the energy transition. We have shown that the largest peaks in solar energy production occur on scales shorter than the 15-minutes of the energy market operates and we have worked on better predictions of these peaks based on KNMI forecasts.

North-Atlantic and Indian Ocean climate variability appears to be tightly related. The observed increase of the amplitude of the North-Atlantic Oscillation (stronger westerlies) over the past decades is directly related to increased atmospheric convection in response to a warming Indian Ocean. Warm Indian Ocean waters flow into the South Atlantic and further northward as part of the global overturning circulation. Paleoceanographic records indicate that this inter-ocean connection around South Africa fluctuated considerably and abruptly in during (inter)glacial change, as southward transport was the only oceanic pathway for the Indian Ocean to dispose of its excess heat. On millennial time-scales that could explain why warming over the North Atlantic coincided with cooling of the Antarctic sector and vice versa. Observations and modeling suggest an important impact of the Indian-Atlantic inter-ocean connection on the strength and stability of the Atlantic overturning circulation, controlled by the (sub)tropical flows feeding it from upstream. These flows converge in the Mozambique Channel and the southern East Madagascar Current (EMC). North Atlantic and Antarctic cold water masses flow in opposite direction in the deep Indian Ocean. To understand their dynamics, an array of moored instruments will measure interannual variability across the Mozambique Channel and remain in operation for several years. A second array will be placed across the EMC. Combined with satellite data and high-resolution ocean-model simulations a complete picture should emerge of the varying flow in the western Indian Ocean presently feeding into the Indian-Atlantic Ocean connection. Further simulations will be executed under both present and glacial conditions, and assessed against new paleorecords of western Indian Ocean climate change over the past 60,000 years from sediment cores. Finally, simulations with the global climate model EC-EARTH will address the processes controlling the global atmospheric and oceanic (tele)connections between the Indian and Atlantic ocean-climate systems, particularly during abrupt North Atlantic climate change.